It has heretofore been common to electrically stimulate nerves for various therapeutic purposes, and medical practitioners have heretofore used electrical stimulation for stimulating muscle activity, relieving pain, and producing sensation, among other therapeutic purposes.
The sequence of effects produced by electrical stimulation, as its intensity is increased, is known to generally follow a pattern of a perception of an electrical sensation (usually tingling), an increase in sensation, fasciculation muscle contraction, pain, and then injury in the form of electrical burns or cardiac arrhythmias.
While therapeutic effects often occur while stimulation is applied with a continuous intensity below that necessary to produce muscle contraction, it should be remembered that exceptions do occur to the general effect pattern such as, for example, when a steady DC current is applied and slowly increased in intensity, muscle contraction cannot be obtained, though the other effects occur in the same order.
Electrical stimulation has been attempted and/or realized through use of a wide variety of electrical waveforms and these waveforms have ranged from a purely DC (galvanic) current or voltage to many different combinations of electrical pulses of various shapes and durations. While at least some such waveforms have provided some degree of desirable effect, the results achieved have been random with no clear understanding of how optimization might, or could, be achieved.
As mentioned above, stimulation has been made to occur with many different types of pulses, and pulse pairs that include both positive and negative pulses have heretofore been suggested (see, for example, U.S. Pat. Nos. 2,375,575, 3,946,745, 4,237,899, and 4,256,116).
While these patents suggest that bi-phased pulse pairs can be utilized for therapeutic purposes, there is no apparent teaching in these patents of devices or methods that are shown to optimize stimulation or enhance stimulation using a symmetrical waveform in conjunction with dual active electrodes. Optimization is important to achieve results with minimum power and maximum effect on functions of the body controlled by the fibers specifically stimulated, and apparatus and method for optimization of stimulation is shown and claimed in U.S. patent application Ser. No. 667,873, entitled "Optimized Nerve Fiber Stimulation", filed Nov. 2, 1984 by Thomas H. Thomson, issued as U.S. Pat. No. 4,640,286 on Feb. 3, 1987, and owned by the Assignee of this invention. This U.S. patent application Ser. No. 009,927 entitled "Nerve Fiber Stimulation Using Plural Equally Active Electrodes", filed Feb. 2, 1987, by Thomas H. Thomson, is a continuation-in-part of U.S. patent application Ser. No. 667,873 (now U.S. Pat. No. 4,640,286), and is owned by the Assignee of this invention. U.S. patent application Ser. No. 009,927 is directed to use of dual active electrodes using bi-phasic waveforms, and this invention utilizes a symmetrical biphasic waveform to stimulate plural active electrodes.